ERT103 MICROBIAL NUTRITION AND GROWTH BY DR ZARINA ZAKARIA School of Bioprocess Engineering

Topic Outline Growth Requirement For Microbes 1. Nutrients:Chemical and Energy Requirements 2. Physical Requirements 3. Ecological Associations

Nutrients: Chemical and Energy Requirements Objectives: To describe the roles of C, H, O, N, trace elements and vitamins in microbial growth and reproduction. To compare the microbes based on their C and energy sources.

i. Carbon (C) requirements From inorganic source (i.e CO2) that called autotrophs. From organic molecules (proteins, carbohydrates) they acquire from other organisms.We called as heterotrophs.

ii. Source of energy - From redox reactions involving inorganic and organic chemicals that called chemotrophs. - From light source that called as phototrophs. -Therefore based on carbon and energy sources, microbes an be categorized into one of four basic groups: i. Photoautotrophs ii. Chemoautotrophs iii. Photoheterotrophs iv. Chemoheterotrophs

iii. Electron requirements or H atoms for hydrogen bonding and electron transfer - From same organic molecules that provide C and energy are called organotrophs. - From inorganic sources (H2, NO2-, H2S) are called lithotrophs.

iv) Oxygen requirements 1. Oxygen is essential for obligate aerobe to serve as final electron acceptor. 2. Oxygen is prohibited for obligate anaerobes. 3. Various concentration of oxygen is unaffected within the two extremes. Microbes in such conditions are called facultative anaerobe.

4. Oxygen tolerance. Do not use aerobic metabolisme but having enzymes that detoxify oxygen’s poisonous forms. Known as aerotolerant anaerobes. 5. Oxygen is required between 2%-10% as found in the stomach. Can be damaged by the 21% of oxygen in the atmosphere. Known as microaerophiles.

v) Nitrogen requirements Nitrogen makes up about 14% of the dry weight of microbial cells. Bacteria such as cyanobacteria and Rhizobium capable to reduce nitrogen gas (N2) to ammonia (NH3) via a process called nitrogen fixation. The bacteria (nitrogen-fixers) provide nitrogen in a useable form to other organisms.

vi) Other Chemical Requirements - Elements such as phosphorus, sulfur, calcium, manganese, magnesium, copper,iron make up 5% of the dry weight of cells. - Other elements, called as trace elements are required in very small amounts. They are such as molybdenum, nickel, selenium and silicon.

2. Physical Requirements Objective: To explain how extremes of temperature, pH and osmotic and hydrostatic pressure limit microbial growth.

Temperature Give effects on the three-dimensional configurations of biological molecules (exp. Proteins and lipids). Hydrogen bonds are temperature sensitive and easily break at higher temperatures caused to proteins denature and lose function. At too low tempt. membranes become rigid and fragile and too high lipids become too fluid and membrane cannot contain the cell or organelle.

                                                                                                                                                                                                                                                                                               

The effects of tempt. On microbial growth: Minimum growth tempt. The lowest tempt. at which microbes are able to conduct metabolism. ii. Maximum growth tempt. The highest tempt. at which microbes continues to metabolize iii. Optimum growth tempt. The tempt. at which microbes’ metabolic activities produce the highest growth rate. Draw figure

Microbes can be categorized into 4 groups based on their preferred tempt. ranges: Psychrophiles Between 0oC-20oC. Optimized at 15oC. In nature, this group live in snowfields, ice and cold water. Can cause food spoilage in refrigerators. ii. Mesophiles - Between 20oC to  40oC.Optimized at  35oC.

- Pathogens to human ( 37oC). Caused food spoilage with inadequate heating during pasteurization. iii. Thermophiles Grow at tempt. above 45oC. in habitats such as compost piles and hot springs. Above 80oC are called hyperthermophiles and can live up to 100oC. Record-holder is Geogemma barossii that can grows and reproduces between 85oC and 121oC. Do not cause disease to human (why?).

ii. pH Microbes can be categorized into 3 groups based on their preferred pH ranges: Neutrophiles - Grow best between pH 6.5 and pH 7.5 and coincidentally the pH range of most tissues and organs in human (what would you expect from this bacteria)

b. Acidophiles - Grow best in acidic habitats. Some can go as low as 0.0 i.e chemoautotrophic bacteria that oxidize sulfur to sulfuric acid. Obligate acidophiles die if pH approaches 7.0. Acid-tolerant microbes can survive without preferring it. c. Alkalinophiles Grow best in alkaline soils and water up to pH 11.5. i.e Vibrio cholerae, the causative agent of cholera grow best at pH 9.0.

iii. Physical effects of water In metabolic processes, water is needed to dissolve enzymes and nutrients and as important reactant. The effects of water on microbes can be discussed in two conditions: Osmotic pressure (OP) The pressure exerted on a semipermeable membrane by a solution containing solute. Related to the concentration of dissolved molecules and ions in solution. Hypertonic, hypotonic and isotonic (T).

Effects of OP on cells: i. Cell placed in hypotonic solution (fresh water) will swell and burst. ii. Cell placed in hypertonic solution (seawater) will die from crenation of its cytoplasm. Microbes grow under high osmotic pressure are called obligate halophiles. Microbes can tolerate high salt concentrations are called facultative halophiles.

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b. Hydrostatic pressure The pressure exerted on a semipermeable membrane by the depth of water level. Every additional 10m of depth, water pressure increases 1 atm. If 100m below, the pressure would be 10 atm. Microbes live under extreme pressure are called barophiles. Their membrane and enzymes depend on pressure to maintain their three-dimensional, functional shapes.

3. Ecologial Associations Objectives: To describe how quorum sensing can lead to formation of biofilms. - Biofilms: complex relationship among numerous individuals, different species, attach as a group to surfaces and display metabolic and structural traits different from those expressed by any of the microorganisms alone. About 65% of bacterial diseases are caused by biofilms. (What is the impacts on scientists?).

Quorum sensing: A process that give result to formation of biofilms in which one bacteria respond to the density of nearby bacteria.